Sand consolidation and gravel packing are two near wellbore techniques widely used for controlling the production of sand from producing wells such as oil wells, gas wells and similar boreholes. In many instances, highly porous and fragmentable sand formations surround a wellbore. Under production conditions, the sand is often displaced from its aggregated structure and carried along by the fluid flood operations to a producing well. If the sand flow is allowed to proceed unchecked, the producing wellbore soon becomes full of sand, thereby clogging the wellbore and impeding oil production. Furthermore, sand arriving at the surface site of the well erodes the production hardware.
As more and more sand is displaced from its original formation, a region of wash-out cavities surrounding the wellbore region results. As the wash-out zones become more extensive, the integrity of the wellbore is threatened and a danger of the wellbore collapsing exists.
It has therefore been the subject of extensive and intense research by the petroleum industry to develop techniques to minimize or obviate displacement of sand particles into producing well areas and prevent the formation of wash-out cavities surrounding the wellbore. One such general approach suggested by the art is to consolidate the coarse sand structures prior to fluid production. Sand consolidation techniques are aimed at cementing loose sand structures adjacent a wellbore. Such consolidation is effective to prevent breakdown of sand formation and subsequent clogging of producing wells.
In many loosely consolidated or unconsolidated formations, it is not economically or practically feasible to consider sand consolidation techniques. Also, there are many instances where substantial wash-out cavities are either initially present naturally near the wellbore or washed-out cavities form around the wellbore after prolonged use despite previous attempts at sand consolidation.
For these conditions, gravel packing techniques are often used to prevent formation sand production or further erosion and to reestablish the integrity of the wellbore periphery. Gravel packing is a secondary sand consolidation technique involving the introduction of a fluid suspension of exogenous particulate matter downhole to fill the wash-out cavities or to "squeeze" to pack into the formation in the vicinity of the well. The term gravel is somewhat loosely applied in the art to encompass hard, rigid particulate matter ranging in size from a coarse sand to pebble size material.
Once the placement of sand and gravel has been accomplished, a slotted liner or "screen" placed as part of the production string helps hold the loose filling material and retards upstream sand flow through the filler material during production conditions.
Gravel packing can be accomplished by several accepted methods. One method is to place a gravel pack in the well adjacent the entire portion of the formation exposed to the well to form a gravel filter. In a cased perforated well, the gravel may be placed inside the casing adjacent the perforations to form an inside-the-casing gravel pack or may be placed outside the casing and adjacent the formation or may be placed both inside and outside the casing. Various such conventional gravel packing techniques are described in U.S. Pat. Nos. 3,434,540; 3,708,013; 3,756,318; and 3,983,941. These patents are incorporated by reference herein. Such conventional gravel packing techniques have generally been successful in controlling the flow of sand from the formation into the well. Sometimes, however, the gravel pack is unable to preclude fines migration which necessitates costly workovers to be initiated.
Therefore, what is needed is a method to prevent fines migration through a gravel pack so as to prevent costly workovers.